122 – Giving a Fifth / Part II, Chapter Twenty (b)
Some authorities say that the halacha that one may not give more than a fifth of his wealth to tzedakah applies only when the person seeks out poor people to give them charity, but if the poor came to him, and they need food or clothing, then one is permitted to feed them their fill and to give them whatever clothing they need, even if the cost will be more than a fifth. According to this opinion, such generosity is an act of piety.
In a life-threatening situation, such as when a Jew is being held captive, and he is likely to die in captivity if he is not redeemed, or if a poor person might die of starvation or other such life-threatening situations, the limit of “a fifth” is not applicable at all, and one must save such people [whatever the cost].